Refrigerating apparatus



Aug. 6, 1963 S. L. DE WITT ETAL.

REFRIGERATING APPARATUS Filed Deo. 29, 1961 2 Sheets-Sheet 1 FL' GG-j-.E//nlllls AAIAIAIIIIIL l vnvnvvvvvv\46 /67 .P -QTYG /DEFROST 60 CL2 l im. TIMER Q2 58\ INVENTORS 741 Smurf L. DeWiH BY Theodore F Dymek.

Allg- 6, 1963 s. L. DE WITT ETAL 3,099,914

REFRIGERATING APPARATUS 2 Sheets-Sheet 2 Filed Dec. 29, 1961 FIG. 2

PIG. 4

INVENTORS Sruan L. Dewi# BY The dore Dymek.

United States Patent 3,099,914 REFRIGERAIlNG APPARATUS Stuart L. De Witt, Villa Park, and Theodore F. Dymek, Elmhurst, Ill., assignors to General Electric Company, a corporation `of New York Filed Dec. 29, 1961, Ser. No. 163,192 7 Claims. (Cl. 62-276) This invention relates to refrigerating apparatus, and especially to frozen food compartment evaporators and the defrosting thereof.

Modern domestic refrigerators are now constructed with a compartment to accommodate fresh foods which are best maintained at temperatures ranging from about 36 F. to 43 F. and a second compartment within which to store frozen foods at a temperature between 0 F. and 10 F. Usually there is a refrigeration evaporator in eachl compartment and an interconnected refrigerating system in which compressed gas is liquilied in a condenser and passes from the condenser 4to the evaporator in the fresh foods compartment. From there refrigerant passes to the frozen food compartment evaporator and then returns to the refrigeration compressor. It is understood that there are refrigerant yexpansion devices such as restrictor tubes upstream of each of the evaporators and a header or accumulator in the circuit between the freezer evaporator and the compressor.

rI'lle compressor may be cycled by a fresh food compartment thermostat which is responsive to the evaporator temperature. The thermostat recloses the cornpressor energy circuit when the evaporator temperature reaches 37 F., and the light coating of frost which may form during a refrigeration cycle will melt. Means are provided to conduct the defrost Water to a place of disposal, usually a pan exposed to the heat of the compressor. By this simple means the water resulting from each of the defrosting operations is evaporated.

The evaporator -in the frozen food compartment also accumulates frost, and because the temperature of the compartment is always below freezing, the frost will not melt during the cycling of the compressor. It is necessary, therefore, to provide means for heating -this evaporator to melt the :frost thereon; said defrosting means usually comprises a heater wire threaded through the heat exchanger fins of the evaporator and the defrosting energizing circuit includes a time clock or the like to activate the defrost system at predetermined times. As further background information for an understand-ing of our invention, it should ybe noted that a blower is used within the freezer compartment to enforce circulation of air over the evaporator.

lt is Well known that when air is circulated through iin and tube type evaporators which are at a temperature substantially lower than 32 F., :frost collects thereon, and in particular frost builds up on those portions of the evaporator against which the air first comes into contact. In conventional lforms of evaporator, such a build-up of frost substantially restricted air ow through the evaporator. In view of the fact that the efficient operation of the refrigeration system requires a constant exchange of heat between the cabinet air and the evaporator, -it is apparent that any blockage of free air ow by a frost accumulation is undesirable. A further disadvantage of conventional n and tube freezer evaporato-rs is that when the evaporator is heated to .melt the frost, the defrost water 4may gather in large drops on the leading edges of the lins, not only reducing the free- .dom of air movement but introducing the possibility that after the defrost operation the resumption of the refrigeration cycle may freeze the residual water to form an immediate blockage against air flow.

The principal object of our invention is to provide an evaporator in which the arrangement and configuration of the leading edges of the heat exchange iins minimizes the possibility that frost build-up or concentration of defrost water can interfere with the substantially -free ow of air -through the evaporator.

Another object of the invention is to provide a refrigeration system inc uding an evaporator in a freezer compartment, a blower to enforce air ow longitudinally throu-gh the evaporator, and a refrigerant header immediately upstream of the evaporator as respects the path of air flow, whereby the header will be the first to accumulate frost and thereby reduce the accumulation of frost on the heat exchange fins of the evaporator.

In a presently preferred form of our inventionl yve arrange the freezer evaporator in vertical disposition against a vertical wall of the freezer chamber. The evaporator ns are perpendicular to the wall and the horizontal passes of evaporator tubing are adjacent that edge of the fins which is remote from the wall. A cover plate immediately in front of the fins and extending from side to side in the freezer compartment provides protection for the evaporator and also serves as a wall of a duct or passage through which air is drawn by means of a suitable fan or blower within the chamber. A first important aspect of our evaporator is that the lins are of two lengths, whereby when assembled with the upper ends thereof in a common horizontal plane, the lower edges of the respective tins are at different vertical levels. Shorter fms are placed intermediate the longer fins, preferably in an alternating relation therewith. The lowermost horizontal pass of evaporator tubing extends only through the bottom portions of the longer fins. The tins are placed approximately 1/s of an inch apart, and it will be apparent that the bottom surfaces of the longer fins, which are the surfaces lirst to intercept the air stream and accumulate frost, will have approximately twice that spacing, considering the thickness of the intervening iin. This spacing can accommodate a substantial frost buildup without seriously restricting air flow through the evaporator.

A second important aspect of our invention is that we dispose a tubular refrigerant header or accumulator in a slightly inclined posture below the freezer evaporator to extend transversely thereof. The header is itself a refrigerated element of substantial area and because it is upstream of the evaporator as respects air flow, the header is the first surface on which frost accumulates. Obviously, the more which can accumulate in a non-critical area as respects air flow, the less opportunity for frost to accumulate on the evaporator fins.

kWe provide electrical resistance heating means in heat transfer relation with the header and the evaporator ns and means for periodically energizing the heater to melt the frost on the header and the evaporator. A third important feature of our invention is that the bottom edge of each of the evaporator fins extends downwardly and rearwardly to a vertex below and toward the rear of the evaporator; in other words, the vertices are substantially to the rear of the runs of evaporator tubing.

, These points are drip points at which the defrost water accumulates for dripping into a trough or the like below the evaporator. `In this way, a build-up of droplets of water over the lower wall surfaces of the fins is prevented.

Other features and advantages of our invention will best be understood by the following description of a presently preferred embodiment read in connection with the accompanying drawings in which:

FIG. 1 is a side sectional elevation of a refrigerator embodying our invention, the section being taken immediately inward of the side wall of the respective upper and lower storage compartments;

FIG. 2 is a side sectional elevation of the rear portion of the frozen food storage space, sectioned as in FIG. 1, but on a larger scale;

FIG. 3 is a fragmentary elevation of the lower portion of the freezer evaporator and header taken on lines 3 3 of FIG. 4;

FIG. 4 is a fragmentary front elevation of the freezer evaportor showing the spacing of fins and the relation thereto of the refrigeration tubing and heater wire. FIG. 4 schematically shows the refrigerant circuit for upper and lower evaporators;

FIG. 5 is a sectional view of the defrost heater; and

FIG. 6 is a schematic wiring diagram for the defrost control.

Referring now to FIG. l, a refrigerator 1 of the combination frozen food-fresh food type has the usual outer cabinet structure 2 of which the fragmentarily shown lower portion 3 provides space for the compressor and other components (not shown). A five-sided inner liner 4 defines the frozen food compartment 5 and a livesided inner liner 6 defines the fresh food compartment 7. The respective compartments have individual doors 8 and 9 hinged and latched pursuant to any conventional mechanism (not shown). It will be understood that the usual thermal insulation is provided between the inner and outer wall structures and that the respective compartments and doors are equipped with the usual shelves, storage baskets and the like (not shown).

The fresh food compartment 7 is provided with a refrigerant evaporator 10 to extract heat therefrom. Said evaporator may be of any conventional type and for simplification, the evaporator 10 is shown in FIG. 4 merely as comprising a sinuous run of tubing 11. Preferably, the evaporator 10 is mounted on the rear wall 12 of the liner 6. The air movement within the chamber 7 is indicated by the arrowed lines as following conventional thermosiphonic convection patterns, although a blower or other forced air circulation means (not shown) may be employed. As will later appear, the cycling of the refrigeration system maintains the compartment 7 in a temperature range of about 36 F. to 43 F., the latter temperature developing during the olf periods of the 'refrigeration system. Any light accumulations of frost which may form on the evaporator during the operation of the refrigeration system will melt during these olf periods, The defrost water is caught in a trough-like pan (not shown) and conducted to a place of disposal, as is well known in the art.

The air in the frozen food compartment is under forced circulation by means of a ,fan 14 driven by a motor 15 housed within a casing 16 above the top wall 17 of the liner 4 as indicated in FIG. 4; the Yfan casing has conventional dellector vanes 18 to diffuse the air as it enters the compartment. The air gives up heat to the freezer evaporator '20; which is arranged in an up right position against the rear Wall 21 of the liner 4, it being understood that the evaporator is secured to the wall by way of ilanges `22 (FIGS. 3 and 4) projecting from :the end fins of the evaporator as later described. The evaporator itself extends almost entirely across the rear of .the compartment `5.

To the evaporator we apply a front cover plate 23 which extends completely across the rear of the compartment 5. This plate 23 lmay be supported forward of the evaporator by lugs or brackets 24 integral with certain of the evaporator plates as suggested in FIG. 3. The plate `23 cooperates with the rear wall Iand the respective side Walls of the liner -4 to establish a Iwide but relatively shallow air passage; the bottom edge of plate 23 is channeled (see 25, FIG. 3) and arranged to form the entry to the air passage. The upper portion 26' of plate 23 extends lforwardly and upwardly intoultimate registration with the top 17 of the liner 4. Substantially centrally of this upper portion as respects the width of the compartment 5, the portion 26 is arranged to accommodate the passage therethrough of the housing 27 yfor the blades of the fan 14. As a means further to direct air into the zone of influence of the fan we may provide a transversely extending deilector baffle 28. The -fan housing deectors `18 accomplish a wide distribution of the air issuing into the Ifreezer compartment 5, but nevertheless the shrouded intake of the fan enforces yan eflicient sweep of air upwardly through the evaporator structure.

lLooking now at FIG. 4, ythe refrigeration system includes any conventional refrigerating compressor 30 from which the compressed refrigerant enters a condenser 31 of any conventional form in which lthe refrigerant is liquelied. The compressor 30 is in the machinery space 3 -below the freezer compartment 5; if the condenser 31 is cooled by -enforced air flow it may also be in that space, and it will be understood that a fan or the like (not shown) is there to enforce the how of the necessary volume of cooling air. iFrequently, however, the condenser is arranged externally of lthe cabinet as by attachment to the rear wall thereof whereupon cooling of the condenser is by natural convection. The type and arrangement of the condenser 31 are no-t material .to the present invention. From the condenser the liquid refrigerant ows into a restrictor tube 32. Because the bore of this tube is measured in thousandths of an inch the art commonly refers to -it as a capillary tube. From this tube the liquid refrigerant discharges into the much larger diameter .tubing 1|1 of the fresh food evaporator. As is well known, as the liquid enters lfrom the restrictor into the evaporator tubing the pressure on .the liquid is sharply reduced. This reduction in pressure establishes a favorable condition for the evaporation of the refrigerant; the heat of the structure and contents of the fresh Ifood compartment provides the heat energy for evaporation or boiling of the `liquid refrigerant in the evaporator tubing. A mixture of liquid and gas leaves the fresh food evaporator at 33, passes through a second restrictor (not shown), and enters the inlet portion 34 of the freezer evaporator 20. The mixture traverses the yseveral runs of tub-ing 35 in which further evaporation takes place and ultimately discharges lfrom the evaporator 20 through the conduit 36 communicating with the accumulator 37 below the evaporator. In its location below the evaporator the accumulator will collect some liquid refrigerant. Because the accumulator is in lthe path of relatively warm air entering the evaporator through the -space 38 below .the cover plate 23, the liquid refrigerant in .the accumulator is undergoing evaporation. Gaseous refrigerant leaves the accumulator through tube 40, which leaves the lfrozen food compartment through the side -wall of the liner 4 and passes `downwardly -along :the restrictor tube 32 and in good heat transfer relation therewith. 'It is understood, of course, that the respective tubes 32 and 40 are located in the insulation between the liner and louter cabinet wall.

The cycling of the compressor is under control of a thermostat having a temperature sensing device in heat transfer rela-tion to lthe fresh food compartment evaporator as later explained. When the cycling of the compressor maintains the Afresh food compartment from 36 to 43 F., the frozen food compartment is maintained in a temperature range of `from about 0 F. to not more than 10 F. Because the evaporator 20 is therefore always at a temperature much below the 'freezing point of water, even during `the olf periods of the compressor, moisture in the air in the lfreezer compartment will condense out on the evaporator 20 in the 'form of frost and cannot melt except 4by the application of additional heat.

Tlhe evaporator 20 is of the iin and tube type, which comprises the most eicient form consistent with mass production techniques. The fins, such as the iin 42, FIG. 3, are formed with slots 43 which are of the keyhole type in that the entrance to the slot is a little narrower than the diameter of the circular base. The tubing 35 is initially of such shape .that it will pass to the base of the slots following which it is compressed to distort it into a shape in which the wall of the tubing is in secure contact with the tins and in good heat transfer relation therewith. For supplying heat -to the evaporator for the defrosting operation each of the -fins is formed with a second arrangement of notches 44 having a substantially circular base dened in part by a short collar or rim 45, FIG. 3. The notches 44 receive runs of a resistance heater 46. As best shown in FIG. 5, the resistance heater wire 47 has conventional insulation 48 `and is contained within a tubular jacket 50 of thin walled aluminum. The heater wire associated with the defrost water 'trough is preferably armored with braided aluminum so as to give it a greater degree of flexibility.

The tins of the evaporator 20 are quite close to each other; actually, in evaponators embodying the present invention the tins are only about 1/5 of an inch apart. Eiiicient operation of the evaporator 20 requiresy that air `ilow through the evaporator be yas free as possibile and it will be apparent that an accumulation of as little as l/s of an inch of frost on the facing surfaces of adjacent iins would seriously obstruct the vertical passage of air between the ns. Such a thickness of frost can readily build up at .the bottom of the tins, for this is the area first encountered by the air as it passes upwardly through the evaporator. Therefore, if frost accumulation obstructs the entry to the passage between the fins, the upper portion of the evaporator loses its efficiency, for its surfaces yare not being scrubbed by moving air.

We construct our evaporator with three forms of plates or tins. The two outermost plates 51, FIGS. 3 and 4, are essentially rectangular and have laterally extending flanges 22 providing at 4least in part the means for mounting the evaporator to the rear wall of the liner 4. Because there are only two suc-h plates 51 their shape and arrangement are relatively unimportant. The plates or fins 42 which are immediately adjacent the tins terminate Well above the bottom of ns 51 as is clear from FIG. 3. Fins 41 then alternate with ns 53, which are substantially longer than the 1ins142. Fins 5?;` terminate immediately above the bottom edge of tins 51. As a manufacturing and performance practice we have the fin 42 shorter than the iin 53 by substantially the width of the tins. In practice this distance is one `and one-half inches. All of the fins have square tops, and it will be understood that with respect to fins 42 and 53 at least, the tops are in common horizontal alignment. The tins 42 and 53 have pointed bottoms, as .shown best in FIG. 2; the

.apex of each said lin, identified as `42.1 and `53.1 respectively, `are rearward of the plane occupied by the convolutions of the evaporator tubing 35. We have found it most advantageous to locate these points 42.1 and 53.1 forward of the rear edge of the tins by about 1A of the total width thereof.

'Ihe result of .this size relationship of the respective tins is that when they `are assembled to constitute the evaporator 20 there is a clearance between adjacent lins in the |lower one and one-half inches thereof of the order of 3%; of an inch, whereupon in the portion of the evaporator which is most likely :to have the heaviest frost accumulate there are suticient air channel spaces to accept a substantial .accumulation of lfrost without air flow obstruction.

An additional important feature of our invention resides in placing the accumulator 37 below and somewhat in front of the evaporator fins, making the accumulator the first cold surface on which frost will collect. In relation to the width of the ins 42 and 53, the evaporator is about one inch in diameter, thus having 4a frost accumulating surface of more than three square inches per inch of length. In View of the fact that the accumulator extends almost the full width of the evaporator,

it presents a very substantial frost-gathering surface.

In a frozen food chamber of six cubic foot volume, which is presently about the maximum volume in refrigerator-freezer combinations, there may be a quite substantial amount of moisture in the air. Because the moisture will condense out in the iirst cold surfaces which it encounters, we are able to remove a substantial part of the moisture by condensation on surfaces where the effect of frost accumulation has very little restrictive effect as respects air flow, for lall of such surfaces are located so as to provide wide air flow channels. rIlherefore, when the air reaches the lower portion of the fins 42, at which location the avail-able air tiow space is only of the order of 1/5 of an inch in width, there is much less moisture in the air and thus a relatively small accumulation of frost on the ns upwardly of that portion. Nevertheless, a Ilight frost will accumulate on the upper part of the evaporator, particularly in humid climates, and we provide means for rapidly defrosting the entire surface of the evaporator. The heating element 46 previously described is arranged for maximum heat concentration at the major areas of frost accumulation. It will be noted in FIGS. 2 iand 4 that a run of the heating element 46 extends along the bottom of the accumulator 37I being yaixed thereto by clamps or the like 54; that it then passes transversely of the evaporator 2b below the lowermost run of evaporator tubing 35; loops back to run beneath the next upper run of evaporator tubing; and back again to nun below the next upper run of tubing. After this, however, the heater wire 46 runs between pairs of evaporator tubing runs.

During a defrosting operation the defrost water trickles ldown the fins until it encounters the sloping drip edges deiining the bottom )of the evaporator fins 42 and 53. The free water will, of course, collect at the respective points 42.1 and 53.1. As previously noted, these drip points are considerably to the rear of the runs 35 of evaporator tub ing. Therefore, we substantially eliminate the possibility of an accumuiation 4of water which might remain on the bottom edges of evaporator fins to re-freeze at the end of the defrost operation, and possibly completely bridge the space between a iin 4Z and its adjacent iin 53. Instead, the large drops of water which form at the drip points drip freely therefrom. A transverse plate 55 directs the Water into a trough 56 which extends the full width of the evaporator'. Saidf trough has an outlet tube 57 which conducts the water into a place of disposition. In 'accordance with well known prior art this place of disposition may be a pan or the llike (not shown) in heat exchange relation with the compressor casing or a loop of tubing through which the hot compressed gas passes kfrom the compressor into the condenser 31. The heat transfer from such loop of tubing is sufficient to evaporate the accumulated water. The trough 56 is itself heated to prevent the water from freezing; we prefer to run a loop of heating element 46 along the upper part of the trough as by confining it within the spun over edges (see FIG. 3) and we additionally bring a loop of the heater tubing :around the outlet tube 57 at its junction with the trough.

Briey reviewing the operation of the refrigeration apparatus prior to lan examination of the control circuit shown in FIG. 6:

During the refrigeration cycle the refrigerant passes from the compressor 36 through the condenser 31, restrictor tube 32, fresh food cooling evaporator 1t), secondary restrictor (not shown), freezer evaporator 20, ac-

cumul-ator 37, and back to the compressor. The compressor is `cycled by means #of a thermostat (schematically shown at 60, FIG. 6) having its sensing element 61 in heat exchange relation with the evaporator 10 to sense the temperatures thereof at its sides and center. This thermostat .is of the constant cut-in type, but has several levels of cutout temperature optionally selectable by the user as known :in the art. Considering one such thermostat setting, for

example, the thermostat will open its contacts 62 at tapproximately 15 F., and re-close them at approximately 37 F. This 37 F. temperature is the constant cut-in temperature of the thermostat. In View of the fact that this temperature represents actual evaporator temperature it is obvious that :any ifrost accumulation on the evaporator 1t) will be melted during each cycling of the thermostat.

The freezer compartment fan 14 circulates air over the evaporator 20 to reduce the temperature of the compartment to a range of from to not more than 10 F. rllhe power circuit to the fan motor is open when the freezer door 3 is lopen; this may be accomplished by a conventional door switch 63 (FIG. 6) which upon being released by the opening door :assumes a normally open position. As will presently appear, the fan motor 15 is deenergized when the compressor is off and during the defrosting period.

'llhe lfreezer defrost system is initiated by a conventional timer 6d, FIG. 6, having a group of switches operated to various relationships by a cam system (not shown) driven by a standard timer motor. FIG. 6 shows the energizing coil 65 of said motor. This timer motor runs only when the compressor is energized and during the defrost operation. rThe gear train (not shown) of the timer completes a rotation 4of the cam shaft in l2 hours; assuming that the compressor will be operating about 50% of the time, the timer will initiate a defrost operation once during each 24 hours.

In further preparation for a discussion of the defrost operation, it should ybe noted that a bimetal thermostat 66 is in heat exchange relation with the freezer evaporator and controls that portion of the heater 46 which is specic to the evaporator; the thermostat 66 is not in a controlling situation with that part of the heater which is disposed about the drain pan 56 or the drain tube 57.

The circuit relationships of FIG. 6 are typical of normal refrigeration operation. Power for the compressor 3'0 may be traced from L1, conductor 67, closed thermostat 60, conductor 68, timer contact '71 to L2. Timer motor 65 is energized by way of conductors 72 and 73 to L2. Freezer fan 15 is operating through conductor 74, closed door switch 63, the closed switch contact stack 75, 70 and 71, to L2. Even though the bimetal thermostat 66 is closed at this time, the respective heaters 46 are in an open circuit because of the open switch contact 76.

When the timer reaches the state of defrost operation, contact 75 will break with contact 70 `and contact 7f1 will break with contact 70 and close against Contact 76. Assuming the thermostat 60 to be closed at this time, the timer motor will remain energized ythrough the obvious circuit, but the compressor circuit will be broken at the open contacts 70 and 72. The circuit for the fan motor 15 will be broken at the open contacts 75 land 70. The respective heating elements 46 are closed by way of closed bimetal thermostat 66 and closed contacts 76, 7,1 to L2. In from eight to ten minutes, if there is a normal frost accumulation on the evaporator 201, the thermostat 66 will sense an evaporator temperature of from 32 to 33 Fahrenheit and will open to interrupt the circuit for the evaporator heating coil. The timer remains on and maintains the contacts 71 and 76 for a further interval. This maintains energy in the drip pan heater to insure that the pan is above freezing temperature until the defrost water has left the pan `and the pipe 57. After a total elapsed time of about eighteen minutes from the start of defrost, the timer opens the contacts 71 and 76 and closes contacts 70 and 71. This deenergizes the drip pan heating element and restarts the compressor. Not until a further time lapse of ve minutes, however, is the contact 75 closed to restore operation of the fan motor 15.

For purposes of simplification yof the circuit the usual other electrical components of a modern refrigerator have been eliminated therefrom. Such components include among others a resistance heater for a butter storage chamber, lights for the respective storage compartments, mullion heaters for prevention of sweating on door areas, etc.

While there has been described what is at present thought to be the preferred embodiment of the invention, it will be understood that various modifications may be made therein and it is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.

We claim yas our invention:

l. In combination:

a refrigerator having a storage chamber to be maintained at a temperature substantially below 32 F.,

a refrigerant evaporator disposed against a wall of said chamber,

said evaporator comprising a plurality of vertically disposed heat exchange ins extending perpendieularly from said wall, said ns being in relatively close sideby-side relation,

certain of said iins being shorter than the others, the shorter fins alternating with the longer tins and the upper edges of all of the fins being in a common plane, whereby the lower portions of successive longer ns are in unobstructed facing relation and are spaced one from the other by at least twice the spacing between adjacent fins,

a plurality of passes of tubing extending horizontally one above the other through said fins adjacent the edge thereof remote from said chamber wall, all of said passes being in series relation and the lowermost of said passes extending only through the bo tom portion of the longer fins,

each of said ns having a lower edge sloping downwardly and rearwardly to an apex below and to the rear of any pass of tubing and forwardly of said chamber wall,

a refrigerant system for circulating refrigerant through said tubing for evaporation therein to reduce the [temperature of said Ins to substantially below the freezing point of the moisture content of the air in said chamber,

means for enforcing a circulation of said air upwardly through the spaces between said fins whereby the lower portion of the longer fin-s will be the rst to accumulate frost and the spacing between adjacent lower portions thereof accommodates such accumulation with minimum obstruction of air flow between all of the fins,

and means for melting the frost from said fins,

the apex portions of the respective fins providing frostwater drip points remote from the passes of tubing.

2. In combination:

ya refrigerator having a storage chamber to be maintained at a temperature substantially below 32 F `a refrigerant evaporator in said chamber,

said evaporator comprising a plurality of vertically disposed elongated heat exchange fins arranged in relatively close side-by-side relation,

certain of said tins being shorter than the others, `the shorter tins yalternating with the longer tins and the upper edges of all of the `fins being in a common plane, whereby the lower portions of successive longer fins are in unobstructed facing relation,

a plurality of passes of tubing extending horizontally one above the other through said tins adjacent the edge thereof facing into said chamber, all of said passes being in series relation and certain of said passes extending only through the bottom portion of the longer fins,

each of said ns having a lower edge sloping downwardly and rearwardly to an apex below and to the rear of a pass of tubing and forwardly of said chamber wall,

ya refrigerant system including said passes of tubing for reducing the temperature of said iins `to below the freezing point of the moisture content of the air in said chamber,

means for enforcing a circulation of said air from below and forwardly of said longer ns yand upwardly over all of said tins and through the spaces therebetween, whereby the lower portion of the longer tins will be the first to accumulate frost and the spacing between adjacent lower portions thereof accommodates such accumulation with minimum obstruction of `air flow between lall of the ns,

and means for periodically melting the frost from said fins,

the apex portions of the respective tins providing frostwater drip points remote from the initial contact of air vwith said ns.

3. In combination:

a refrigerator having a storage chamber to be maintained at a temperature substantially below 32 F.,

a refrigerant evaporator disposed against a rear wall of said chamber,

said evaporator comprising a plurality of elongated vertically disposed heat exchange fins extending perpendicularly from said wall, said fins being in relatively close side-by-side relation,

certain of said ns being shorter than the others, the shorter fins alternating with the longer ns and the upper edges of all of the tins being in a common plane, whereby the lower portions of adjacent longer tins are in unobstructed facing relation,

la plurality of passes of tubing extending one above the other through said tins adjacent the edge thereof remote from -said chamber wall, all of said passes being in series relation,

a cover plate for said evaporator, said plate combining with side and rear walls of said chamber Ato consti- 4tute an air ilow passage about said evaporator, the lower edge of said plate being spaced from the bottom of said chamber to provide a transversely extending entrance to said :air flow passage below and `forwardly of said longer ns,

a refrigerant system for circulating refrigerant mthrough said tubing for evaporation therein to reduce the temperature of said -fins to below the dew point of the air in said chamber, said refrigerant system including a refrigerant accumulator disposed in the path of air flow into said air ow passage,

means for enforcing a circulation of said air upwardly through said passage whereby the accumulator and the lower portion of the longer fins will be the first to accumulate frost and Ithe spacing between adjacent lower portions of said tins accommodates such accumulation with minimum obstruction of air ilow between the tins,

and electric resistance means for periodically melting the frost from said lins,

Isaid resistance means providing a concentration of heat in the lower portion of said tins and at the accumulator.

4. In combination:

a refrigerator having a storage chamber to be maintained at a temperature substantially below 32 E,

a refrigerant evaporator disposed against 'a vertical wall of said chamber,

said evaporator comprising a plurality of elongated vertically disposed heat exchange tins extending perpendicularly from said wall, said fins being in relatively close side-by-side relation,

certain of said fins being shorter than the others, the shorter tins alternating with the longer fins and the upper edges of all of the ns being in a common plane, whereby the lower portions of successive longer fins are in unobstructed facing relation,

a plurality of passes of tubing extending one above the other through said tins adjacent fthe edge thereof l0 remote from said chamber wall, all of said passes being in series relation,

a cover plate for said evaporator, said plate combining with walls of said chamber to enclose said evaporator in an air flow passage, the lower edge of said plate being spaced from the bottom of said chamber to provide a transversely extending entrance to said passage, said entrance being below and forwardly of said tins,

a refrigerant system for circulating refrigerant through said tubing for evaporation therein to reduce the temperature of said fins to .substantially below 32 F., said system including a refrigerant accumulator extending transversely within said air entrance passage below iand forwardly of said ns,

means including a blower 4for enforcing a circulation of said air upwardly through said air flow passage, whereby said accumulator and` the lower portion of the longer iins will be the first to be contacted by air owing from said chamber into said air flow passage, whereby frost will accumulate on said accumulator and fins,

land means including a resistance beater in beat exchange relation with said fins and said accumulator for melting any frost which has formed thereon.

5. An evaporator for the freezer compartment of a refrigerator, comprising, in combination:

a. plurality of first elongated metal -iins rhaving a pointed bottom edge,

a plurality of second elongated metal tins having a pointed bottom edge, said second iins being longer .than the ii-rst,

said first and second tins being disposed in an upright posture within said compartment with the bottom edges thereof facing the bottom of said compartment and the front edges thereof facing the front of said compartment,

the apex of the pointed bottom .of each said fin being disposed substantially closer to the rear edge of said fm than to the front edge thereof,

means for supporting the respective pluralities of tins in relatively close parallel relation, said ns being arranged 4with their top edges uniformly spaced from the top of said compartment and the bottom edge of the shorter tins closer to the immediately adjacent iin than the bottom edge of the longer fins is to the immediately adjacent longer tin,

said supporting means including a plurality of passes of tubing extending transversely through said fins relatively close to the front edge thereof, the lowermost pass of tubing extending only through the lower portion of the llonger tins, said passes of tubing being serially interconnected,

means for introducing refrigerant into the lowermost pass of tubing,

a refrigerant accumulator extending transversely of aid evaporator below rand forwardly of said longer means for conducting refrigerant from the uppermost pass of tubing into said accumulator,

and means for conducting refrigerant from said accumulator to a .refrigerant compression mechanism.

6. An evaporator for the freezer compartment of a refrigerator, comprising, in combination:

a plurality of elongated metal fins having a pointed bottom edge, said fins being disposed in an upright posture within said compartment with the bottom edges thereof facing the bottom of said compartment and the front edges thereof facing the front of said compartment, the apex of the pointed bottom of each said iin being disposed substantially closer to the rear edge of said iin than to the front edge thereof, means for supporting the fins in relatively close parallel relation to establish lair liow passages therebetween,

1 1' said lins being arranged with the bottom edge of levery other n extending below the bottom edge of the immediately adjacent iin by an amount substantially equal to the Width of the fins,

said supporting means including a plurality of passes of tubing extending transversely through said ns relatively close to the front edge thereof, said passes of tubing being serially interconnected,

means for introducing refrigerant into the lowermost pass of tubing,

a refrigerant accumulator extending transversely of said evaporator below and forwardly of said downwardly extending fm portions,

means -for conducting refrigerant from the uppermost pass of tubing into said accumulator,

and means for conducting refrigerant from said laccumulator to a refrigerant compression mechanism.

7. In combination:

wall structure defining a chamber to be maintained at a temperature substantially below 32 F.,

ya refrigerant evaporator comprising a plurality of elongated heat exchange yfins in spaced side-by-side relation,

certain of said ns being substantially longer than the others, `short and long ns being in an lalternating relationship and disposed in a manner whereby the lower portions of :successive longerv ns are in unobstructed facing relation,

the .bottom portion of each of the longer iins being V-shaped with the tip thereof being much closer 4to one of the longer edges of the iin than to the opposite edge,

refrigerant conduit means extending through all of i said ns in a plurality of serially interconnected passes disposed in a common plane adjacent the said opposite edge of said ns,

means for supporting said evaporator with the firstnamed longer edge of each of said -ns in relatively close parallel relationship to a vertical Wall, of said chamber and the said opposite edge occupying la common vertical plane,

.a plate extending transversely of said evaporator in covering relation thereto, said plate being disposed forwardly of said evaporator considered with respect to said vertical chamber wall and defining with said wall and the top wall of said chamber -a duct for channelling air ow longitudinally of said fins,

said plate being confgurated to provide an elongated air entrance `below and forwardly of said evaporator structure,

Ia refrigerant `accumulator of cylindrical shape extending ysubstantially horizontally across said evaporator in the plane of said runs of conduit Ibetween said fair entrance and the bottom portion of said longer fins, the dia-meter of said evaporator lbeing substantially less than the transverse dimension of said tins,

-means for pumping refrigerant in a closed circuit through said evaporator and said accumulator,

and fan means disposed in said duct above and forwardly of said evaporator to cause air to flow into said inlet passage and to discharge into said chamber adjacent the upper wall thereof.

References Cited in the file of this patent UNITED STATES PATENTS 2,099,665 Smith NOV. 16, 1937 2,484,588 Richard Oct. ll, 1949 2,767,558 Wallenbrock Oct. 23, 1956 2,798,366 Erl July 9, 1957 2,923,135 Preotle Feb. 2, `1960 2,967,404 Detwiler Jan. 10, 196,1 

6. AN EVAPORATOR FOR THE FREEZER COMPARTMENT OF A REFRIGERATOR, COMPRISING, IN COMBINATION: A PLURALITY OF ELONGATED METAL FINS HAVING A POINTED BOTTOM EDGE, SAID FINS BEING DISPOSED IN AN UPRIGHT POSTURE WITHIN SAID COMPARTMENT WITH THE BOTTOM EDGES THEREOF FACING THE BOTTOM OF SAID COMPARTMENT AND THE FRONT EDGES THEREOF FACING THE FRONT OF SAID COMPARTMENT, THE APEX OF THE POINTED BOTTOM OF EACH SAID FIN BEING DISPOSED SUBSTANTIALLY CLOSER TO THE REAR EDGE OF SAID FIN THAN TO THE FRONT EDGE THEREOF, MEANS FOR SUPPORTING THE FINS IN RELATIVELY CLOSE PARALLEL RELATION TO ESTABLISH AIR FLOW PASSAGES THEREBETWEEN, SAID FINS BEING ARRANGED WITH THE BOTTOM EDGE OF EVERY OTHER FIN EXTENDING BELOW THE BOTTOM EDGE OF THE IMMEDIATELY ADJACENT FIN BY AN AMOUNT SUBSTANTIALLY EQUAL TO THE WIDTH OF THE FINS, SAID SUPPORTING MEANS INCLUDING A PLURALITY OF PASSES OF TUBING EXTENDING TRANSVERSELY THROUGH SAID FINS RELATIVELY CLOSE TO THE FRONT EDGE THEREOF, SAID PASSES OF TUBING BEING SERIALLY INTERCONNECTED, MEANS FOR INTRODUCING REFRIGERANT INTO THE LOWERMOST PASS OF TUBING, A REFRIGERANT ACCUMULATOR EXTENDING TRANSVERSELY OF 